1. Technical Field
The present invention relates to image display apparatus and, more particularly, to a multiview three-dimensional image display apparatus.
2. Description of the Related Art
All three-dimensional image display apparatus, other than those that provide true tree-dimensional images, provide only an illusion of three-dimensionally, since these apparatus form viewing zones on two-dimensional surfaces, such as the screen of a cathode ray tube. On such two-dimensional surfaces, images of an object captured from a plurality of perspectives are separated in space and time by intervals dictated by the space- or time-multiplexed technique employed to capture the images.
The viewing zone comprises a plurality of sub-zones, where each sub-zone corresponds to a different one of the desired perspectives of the object and each sub-zone comprises two regions separated by a distance less than the separation of the eyes of the viewer. A viewer who fixes his eyes on the viewing zone visually experiences the sensation of depth, since images of the object captured from two different perspectives impinge on the viewer""s right and left retinas.
In a contact-type three-dimensional image display apparatus, a flat optical element, such as a lenticular plate or parallax barrier plate, is disposed immediately adjacent a flat display and a sensation of three-dimensionality is provided by use of a space-multiplexed technique to capture the images. In a space-multiplexed imaging technique, the resolution of each of multiview image frames is reduced to be the number of view points without changing the rate at which the images are captured, and each of the multiview image frames is sequentially repeated and combined on a pixel basis to be merged into one image frame so that the merged image frame may be displayed on a display. The function of the optical element is to classify images from the multiple viewpoints, which are mixed in a periodic pattern and displayed on the display, into each group of images from the same viewpoints, resulting in the images in the same group being combined and displayed at the viewing zone.
In a projection-type three-dimensional image display apparatus, an optical element is used to project images onto a display screen and the sensation of volume derives from use of a time-multiplexed technique to capture the images. In a time-multiplexed imaging technique, images captured from multiple perspectives are sequentially displayed at a certain field rate and a spatial display interval for which one field image of multiview images is displayed is equal to a field period of a planar image divided by the number of multiview images in a viewing zone. In order to divide the viewing zone into multiple regions, each of which corresponds to a different one of the multiple perspectives of the object, the aperture of the optical element is effectively divided by use of a liquid-crystal shutter plate disposed immediately adjacent the optical element. The shutter plate includes a plurality of regularly spaced, substantially parallel strip-type shutters, where the number of strip-type shutters is the same as the number of perspectives. The strip-type shutters are opened and closed in synchronization with the display sequence and period of a field image from each viewpoint.
CRT displays may be utilized in both contact- and projection-type three-dimensional image display apparatus that include an optical element. Contact-type display apparatus have the advantage of small size, although:
(1.) brightness of the display is relatively low, since the viewing zone is widely spread at the front of the optical element;
(2.) viewers typically experience eye strain, since they must focus their eyes on a constant position due to the small viewing zone;
(3.) viewers typically become confused when they move their eyes, since alternating orthoscopic and pseudoscopic viewing zones are viewed due to eye movement.
Projection-type apparatus are bulky and require use of a liquid-crystal shutter to divide the aperture of the optical element in order to display images. Furthermore, a apparatus using an optical element, except for a holographic screen, can be used only with difficulty as a multi-viewer apparatus due to the restriction of a viewing zone location. These difficulties may be ameliorated by using an eye-tracking technique or by forming a plurality of viewing zones. It is however difficult to solve these problems completely since they stem from the characteristics of the optical element.
The object of the present invention is accordingly to provide a multiview three-dimensional image display apparatus that utilizes a time-multiplexed imaging technique to improve the notoriously low brightness of conventional projection- and contact-type image display apparatus due to the widely-spread viewing zone at the front of an optical element.
Another object of thee present invention is to provide a multiview three-dimensional image display apparatus on which multiple viewers may simultaneously view the same three-dimensional image.
According to one embodiment of the present invention, a multiview three-dimensional image display apparatus comprises: a light source; a shutter plate for selectively passing light from the source; a diffuser immediately adjacent the shutter plate for uniformly diffusing light from the shutter plate; an optical element disposed on the optical path from the diffuser for forming a viewing zone; and a transparent display immediately adjacent the optical element for displaying multiview images, wherein the multiview images are displayed based on a time-multiplexed technique and the Viewing zone in formed at the front of the transparent display.
According to another embodiment of the present invention, a multiview three-dimensional image display apparatus comprises: a plurality of independent light sources; a shutter plate for selectively passing light from the source; a diffuser immediately adjacent the shutter plate for uniformly diffusing light from the shutter plate; an optical element for imaging light from the diffuser and for forming a plurality of viewing zones; and a transparent display immediately adjacent the optical element for displaying multiview images, wherein the multiview images are displayed based on a time-multiplexed technique and the plurality of viewing zone s are formed at the front of the transparent display.